U.S. patent application number 11/087568 was filed with the patent office on 2005-08-25 for pulsed laser beam machining method and apparatus for machining a wiring board at multiple locations.
This patent application is currently assigned to MITSUBISHI DENKI KABUSHIKI KAISHA. Invention is credited to Fukushima, Tsukasa, Kaneko, Masayuki, Kurosawa, Miki, Mizuno, Masanori, Moriyasu, Masaharu, Takeno, Shozui.
Application Number | 20050184035 11/087568 |
Document ID | / |
Family ID | 24771257 |
Filed Date | 2005-08-25 |
United States Patent
Application |
20050184035 |
Kind Code |
A1 |
Kurosawa, Miki ; et
al. |
August 25, 2005 |
Pulsed laser beam machining method and apparatus for machining a
wiring board at multiple locations
Abstract
In a laser beam machining method for a wiring board, a machined
portion of the wiring board is irradiated with a pulsed laser beam
for a beam irradiation time ranging from about 10 to 200 .mu.s and
with energy density of about 20 J/cm.sup.2 or more, thereby
machining the wiring board, for example, drilling for a
through-hole and a blind via hole, grooving, and cutting for an
outside shape. The laser beam operates at a frequency of more than
67 Hz, and the spot of the laser beam is sequentially moved to
different drilling positions for each pulse. After all of many
drilling positions in the range of a scan vision are irradiated
with the laser beam pulse by pulse, or after the elapse of a time
of 15 ms or more from irradiation of the first drilling position,
the laser spot is returned to the first drilling position. The spot
is sequentially moved once again, and the movement is repeated
several times. A pause of 15 ms or more is required between pulses
directed to the same drilling position to avoid formation of a
thick char layer and projection of glass cloth into the hole.
Inventors: |
Kurosawa, Miki; (Tokyo,
JP) ; Fukushima, Tsukasa; (Tokyo, JP) ;
Mizuno, Masanori; (Tokyo, JP) ; Takeno, Shozui;
(Tokyo, JP) ; Moriyasu, Masaharu; (Tokyo, JP)
; Kaneko, Masayuki; (Tokyo, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
MITSUBISHI DENKI KABUSHIKI
KAISHA
|
Family ID: |
24771257 |
Appl. No.: |
11/087568 |
Filed: |
March 24, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11087568 |
Mar 24, 2005 |
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09994719 |
Nov 28, 2001 |
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09994719 |
Nov 28, 2001 |
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09549498 |
Apr 14, 2000 |
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6373026 |
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09549498 |
Apr 14, 2000 |
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08690140 |
Jul 31, 1996 |
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Current U.S.
Class: |
219/121.61 ;
219/121.69; 219/121.71; 219/121.72; 219/121.8 |
Current CPC
Class: |
H05K 3/0032 20130101;
H05K 2203/0554 20130101; H05K 2203/081 20130101; B23K 26/389
20151001 |
Class at
Publication: |
219/121.61 ;
219/121.71; 219/121.72; 219/121.69; 219/121.8 |
International
Class: |
B23K 026/38 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 7, 1995 |
JP |
201194/95 |
Mar 15, 1996 |
JP |
059862/96 |
Claims
1-22. (canceled)
23. A laser beam machining method, for performing machining
operations on a wiring board made of a composite material of
organic and inorganic materials by use of a laser beam, the method
comprising the step of: at a time of pulse irradiation with the
laser beam while sequentially positioning a spot of the laser beam
at target positions on the wiring board in synchronization with a
pulse frequency of the laser beam, providing a time interval of 15
ms or more between successive pulsed laser beams, having a pulse
frequency of 67 Hz or more and a beam irradiation time ranging from
10 to 200 .mu.s, for irradiation of the respective target position
irrespective of the pulse frequency by irradiating another target
position with a pulsed laser beam outputted for the time interval
therebetween.
24. A laser beam machining apparatus, for performing machining
operations on a wiring board made of a composite material of
organic and inorganic materials by use of a laser beam radiated
from a laser oscillator, the apparatus comprising; optical means
for changing a direction of the laser beam and moving the laser
beam on the wiring board while sequentially positioning a spot of
the laser beam at target positions on the wiring board, and control
means for synchronous control between a pulse oscillating operation
of the laser oscillator and an operation of the optical means, and
for control of the optical means such that a time interval is set
to 15 ms or more between successive pulsed laser beams, having a
pulse frequency of 67 Hz or more and a beam irradiation time
ranging from 10 to 200 .mu.s, for irradiation of the target
positions irrespective of a pulse frequency of the laser
oscillator.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a machining method for a
wiring board and a machining apparatus for a wiring board employing
a laser beam for machining such as drilling for a through-hole, an
inner via hole, and a blind via hole, grooving, and cutting for an
outside shape of the wiring board referred to as so-called printed
board, and more particularly to a machining method for a wiring
board and a machining apparatus for a wiring board in which a fine
conduction hole can rapidly and accurately be formed, and a
carbonic acid gas laser oscillator to generate a pulsed laser beam
most suitable for the above machining.
[0003] 2. Description of the Prior Art
[0004] A printed board includes a plurality of insulating base
materials with conductor layers, stacked and joined in a
multi-layer fashion. Among the conductor layers applied onto the
insulating base materials, the optional conductor layers in a
vertical direction are electrically connected through conduction
holes referred to as a through-hole, an inner via hole, and a blind
via hole. FIG. 33 is a sectional view of such a conventional
multi-layer printed board. In the drawing, reference numeral 51
means a printed board, 52 to 56 are conductor layers, 57 is
metallic deposits, 61 to 64 are insulating base materials, and 65
to 68 are conduction holes. In the five-layer printed board 51
including the conductor layers 52 to 56, the insulating base
materials 61 and 63 with both sides coated with copper foil and the
conductor layer 56 including copper foil are stacked and joined by
using the insulating base materials 62 and 64 referred to as
prepreg, and the conduction holes 65 to 68 are provided to pass
through the conductor layers 52 to 56.
[0005] As shown in FIG. 33, the conduction hole 65 is mounted for
conduction between the conductor layer 52 and the conductor layer
53 in the insulating base material 61, and the conduction hole 66,
referred to as blind via hole (BVH), is mounted for conduction
between the conductor layer 52 in the insulating base material 61
and the conductor layer 54 in the insulating base material 63. The
conduction hole 67, referred to as inner via hole (IVH), is mounted
for conduction between the conductor layer 54 and the conductor
layer 55 in the insulating base material 63. The conduction hole
68, referred to as through-hole (TH), is mounted for conduction
between the conductor layer 52 in the insulating base material 61
and the conductor layer 56 stacked and joined through the
insulating base material 64.
[0006] The conduction holes 65 to 68 shown in FIG. 33 are holes
machined by a drill. Further, after drilling, the conduction holes
are plated through the metallic deposits 57, and the conductor
layers are electrically connected.
[0007] In the prior art, a machining method for the conduction hole
includes, for example, drill machining using a rotary milling
cutter. Further, a machining method for grooving or cutting for an
outside shape includes, for example, router machining using a
rotary milling cutter. On the other hand, in recent years, higher
density wiring has been desired for higher performance of an
electronic device. A more multi-layered and smaller printed board
is required to meet the above requirement. Further, it is essential
to provide a finer hole diameter of the conduction hole for this
purpose. With the current state of the art, the conduction hole is
generally provided in the printed board by the mechanical method
using the drill. However, the method has drawbacks in that the
finer hole diameter is limited, for example, drilling for a hole
diameter of .phi. 0.2 mm or less is very difficult to cause heavy
wear of the drill such as breakage, resulting in poor productivity
due to a long time required for replacement of the drill. Further,
it is difficult to simultaneously machine adjacent positions,
thereby requiring a considerable machining time. In addition, the
insulating base material has a thickness of 0.1 mm or less because
of the smaller printed board. Since it is difficult to control a
hole depth in the drill machining with accuracy of 0.1 mm or less,
it is difficult to form the blind via hole in such a thin-walled
insulating base material. Further, in order to realize cost
reduction by the smaller printed board and an increase in yield,
the grooving and the cutting for the outside shape require an
accurate depth control in the grooving, a narrower cutting width,
and cutting after parts are packaged. However, the mechanical
methods such as router machining are unpractical since the above
limitation is similarly imposed thereon.
[0008] Instead of the machining methods for the printed board
including the above mechanical methods, attention has been given to
methods, which have partially been put to practical use, employing
a laser beam such as an eximer laser or carbonic acid gas laser,
disclosed in IBM Journal of Research and Development, Vol. 126, No.
3, pp. 306-317 (1982), and Japanese Patent Publication (Kokoku) No.
4-3676. These laser beam machining methods utilize a difference in
absorption coefficient of light energy such as the eximer laser or
the carbonic acid gas laser between resin or glass fiber serving as
the insulating base material forming the printed board, and copper
serving as the conductor layer. For example, since almost the
entire laser beam emitted from the above laser can be reflected at
the copper, a copper foil removed portion having a required
diameter is formed in top copper foil through etching and so forth,
and the copper foil removed portion may be irradiated with the
laser beam. It is thereby possible to selectively decompose and
remove the resin and the glass so as to form a fine through-hole
and a fine inner via hole in a short time. If internal-layer copper
foil is previously stacked in a machined portion, the decomposition
and the removal of the insulating base material are terminated at
the internal-layer copper foil. It is thereby possible to form a
blind via hole which can surely be terminated at bottom copper
foil. There is an advantage of no wear of the tool such as breakage
because the laser beam machining methods are contactless machining
methods.
[0009] The above laser beam machining methods employ a pulse laser
such as the eximer laser and a TEA-carbonic acid gas laser, with an
extremely narrow pulse width of 1 .mu.s or less. The pulse laser
can finely divide into chips (1) a single base material made of
high polymeric material such as polyimide, or epoxy, (2) a
composite material reinforced by aramid fiber or the like,
containing the polyimide, the epoxy, and so forth, and (3) an
inorganic material such as glass. It is thereby possible to rapidly
and accurately form a good machined hole with a smooth machined
portion and less altered layer in a printed board in which as the
insulating base material is used composite material dispersed in
the polyimide, the epoxy, and so forth.
[0010] The conventional laser beam machining method for the wiring
board has the above structure. The eximer laser or the TEA-carbonic
acid gas laser is used to provide the through-hole and the inner
via hole in the most commonly used printed board having the
insulating base material made of glass cloth containing the glass
fiber and the resin, such as a glass epoxy printed board referred
to as FR-4 made of the glass cloth and epoxy resin. In this case,
there are problems in that metallic deposit for conduction can not
easily be coated on a hole inner wall due to the extremely rough
inner wall of the hole, and reliability of the metallic deposit can
not be ensured. The problems are generated because the insulating
material of the printed board is not only the composite material
made of organic material and inorganic material but also
heterogeneous material in which the organic material and the
inorganic material are contained in clusters to some extent.
[0011] Further, there is another problem in that a uniform machined
hole can not be provided due to differences in, for example,
absorption coefficient of the laser beam, decomposition
temperature, and thermal diffusivity between an organic material
portion and an inorganic material portion. For example, since a
wavelength of the laser beam in the eximer laser can not easily be
absorbed by the glass, sufficient energy for decomposition of the
glass can not be supplied so that a glass portion is difficult to
remove, resulting in a problem of a rough machined hole. On the
other hand, both the resin and glass can show high absorption
coefficient in case of the TEA-carbonic acid gas laser. However,
when energy density of 20 J/cm.sup.2 required to efficiently
machine glass epoxy material is obtained in the TEA-carbonic acid
gas laser, excessively high power density of 2.times.10.sup.7
W/cm.sup.2 or more is caused due to the narrow pulse width of 1
.mu.s or less. Such high power density may easily cause plasma at
the machined portion. Once the plasma is formed, laser energy is
absorbed by the plasma, resulting in insufficient energy reaching
the machined portion. Hence, it is difficult to remove glass having
a high decomposition temperature, thereby causing a problem of the
rough machined hole.
[0012] If the energy density is set to cause no plasma, the
machining progresses extremely slowly, resulting in a problem of a
reduction in productivity.
[0013] In addition, only when a beam diameter is larger than the
machined portion, good machining may be made to the materials (1),
(2), and (3) in the conventional laser beam machining method.
Otherwise, if the machined portion is larger than the beam
diameter, for example, in case of cutting, grooving, and drilling
for a large diameter hole, a removed material caused at a beam
irradiated portion adheres to a position other than the beam
irradiated portion. As a result, after the machining, the machined
portion is coated with additionally deposited soot, thereby
reducing reliability of insulation and reliability of metallic
deposit in the printed board. Hence, there is another problem of
the need for the step of, for example, complicated after-treatment
such as wet etching.
[0014] Other than the extremely short pulse laser such as the
eximer laser and the TEA-carbonic acid gas laser, there are other
laser beam machining methods for the wiring board, using a typical
carbonic acid gas laser of high-speed axial-flow type or three-axes
orthogonal type in the prior art. In the conventional carbonic acid
gas lasers, more importance is given to a CW output characteristic
than a pulse output characteristic to enhance oscillation
efficiency. That is, there is in theory a problem of pulse response
sensitivity at a time of pulse oscillation, in particular, a
characteristic in which a time is required for a fall of a laser
pulse. Thus, the machining by the conventional carbonic acid gas
laser having such a characteristic results in irradiation of the
machined portion with a laser beam for a longer time, thereby
causing a gradual temperature gradient around the machined portion.
As a result, as shown in FIG. 34, a larger difference is caused in
amount of removal between the resin and the glass due to a
difference in decomposition temperature therebetween. When only the
resin is excessively removed, there are problems in that projection
of the glass fibers results in a rough machined hole as shown in
FIG. 35, and the long heating time generates a char layer on a wall
surface of the hole.
[0015] Further, carbides are generated around the machined portion,
and the laser beam is absorbed by the copper through the carbides,
resulting in frequent damage to the copper foil as shown in FIG.
36. Hence, there is a problem in that the blind via hole is
difficult to form in the above laser beam machining methods.
[0016] Though descriptions have been given of the machining for the
hole, the same problems are caused in the grooving and the
cutting.
SUMMARY OF THE INVENTION
[0017] In order to overcome the above problems, it is an object of
the present invention to provide a stable laser beam machining
method for a wiring board, in which a printed board with an
insulating base material containing cloth-like glass fibers can
rapidly and accurately be machined, for example, drilled for a
through-hole, an inner via hole and a blind via hole, grooved, or
cut for an outside shape without roughness of a machined portion
and the need for complicated after-treatment of additional deposit,
and no damage is caused to copper foil, and to provide a laser beam
machining apparatus for a wiring board, for realizing the laser
beam machining method for the wiring board and improving
productivity.
[0018] It is another object of the present invention to provide a
carbonic acid gas laser oscillator for machining a wiring board,
which can output a laser beam with a pulse width most suitable for
the laser beam machining method for the wiring board.
[0019] According to one aspect of the present invention, for
achieving the above-mentioned objects, there is provided a laser
beam machining method for a wiring board, including the step of
irradiating a machined portion of the wiring board with a pulsed
laser beam for a beam irradiation time ranging from 10 to 200 .mu.s
and with energy density of 20 J/cm.sup.2 or more.
[0020] According to another aspect of the present invention, there
is provided a laser beam machining method for a wiring board,
including the step of irradiating the same machined portion of the
wiring board with a pulsed laser beam with intervals of a beam
irradiation pausing time of 15 ms or more and energy density of 20
J/cm.sup.2 or more.
[0021] According to still another aspect of the present invention,
there is provided a laser beam machining method for a wiring board,
including the steps of combining into one pulse group laser beams
including a plurality of pulses having energy density of 20
J/cm.sup.2 or more and generated at intervals of a predetermined
beam irradiation pausing time, and irradiating the same machined
portion of the wiring board with a pulsed laser beam with the
plurality of pulse groups respectively including the plurality of
pulses at intervals of a pulse group interval irradiation pausing
time longer than the predetermined beam irradiation pausing time.
Preferably, the predetermined beam irradiation pausing time is 4 ms
or more, the number of pulses in the pulse group is 4 or less, and
the pulse group interval irradiation pausing time exceeds 20
ms.
[0022] According to a further aspect of the present invention,
there is provided a laser beam machining method for a wiring board,
including the step of, at a time of scanning a surface of the
wiring board while irradiating a machined portion of the wiring
board with the pulsed laser beam, scanning by a laser beam such
that the machined portion is not continuously irradiated with the
laser beam over 4 pulses at intervals of a beam irradiation pausing
time less than 15 ms.
[0023] According to a still further aspect of the present
invention, there is provided a laser beam machining method for a
wiring board, including the steps of providing a 1 mm beam diameter
on a surface of a machined portion, and scanning a surface of the
wiring board at a scanning speed ranging from 8 to 6 m/min while
irradiating the machined portion with a laser beam for a beam
irradiation time ranging from 10 to 200 .mu.s and at intervals of a
beam irradiation pausing time of 2.5 ms.
[0024] According to another aspect of the present invention, there
is provided a laser beam machining method for a wiring board,
including the steps of setting a laser beam to have a square spot
effective in machining of a machined portion of the wiring board,
and scanning a surface of the wiring board while irradiating the
machined portion of the wiring board with the pulsed laser beam.
Preferably, the square spot of the laser beam on the machined
portion is set to have a size of 0.9 mm.times.0.9 mm, and the
surface of the wiring board is scanned with a scanning speed of 6
m/min and a scanning pitch of 200 .mu.m while the machined portion
being irradiated with the laser beam for a beam irradiation time
ranging from 10 to 200 .mu.s and at intervals of a beam irradiation
pausing time of 1.25 ms.
[0025] According to a further aspect of the present invention,
there is provided a laser beam machining method for a wiring board,
including the steps of previously removing a metallic layer on the
wiring board at a portion corresponding to a machined portion of
the wiring board, forming a base material removed portion through
machining by irradiating a base material of the machined portion
with a laser beam through the metallic layer removed portion, and
additionally irradiating the base material removed portion and a
periphery of the base material removed portion, or only the
periphery of the base material removed portion with a laser beam.
Preferably, the additionally irradiated laser beam has a smaller
peak output than a peak output of the first laser beam, and is used
to scan at a higher scanning speed than a scanning speed during
first laser beam irradiation.
[0026] According to a further aspect of the present invention,
there is provided a laser beam machining method for a wiring board,
including the step of, at a time of previously removing a metallic
layer on the wiring board at a portion corresponding to a machined
portion, partially removing the metallic layer such that a laser
beam can reach only an outer periphery of a base material removed
portion to be formed by irradiating a base material of the machined
portion with the laser beam. Preferably, a surface of the wiring
board is scanned with a scanning speed of 8 m/min and a scanning
pitch of 100 .mu.m while the machined portion being irradiated with
the laser beam for a beam irradiation time ranging from 10 to 200
.mu.s and at intervals of a beam irradiation pausing time of 2.5
ms.
[0027] According to a further aspect of the present invention,
there is provided a laser beam machining method for a wiring board,
including the steps of previously removing a metallic layer on the
wiring board at a portion corresponding to a machined portion of
the wiring board, and flowing a gas in a direction from a laser
beam scanning start point to a laser beam scanning end point in the
machined portion at a time of machining by irradiating a base
material of the machined portion with a laser beam while scanning
by the laser beam through the metallic layer removed portion.
[0028] According to a further aspect of the present invention,
there is provided a laser beam machining method for a wiring board,
including the steps of forming a metallic layer having a desired
shape by partially removing the metallic layer by pulse irradiation
with a laser beam having sufficient intensity to melt and remove
the metallic layer on the wiring board, and additionally
irradiating a machined portion of the wiring board through a
metallic layer removed portion with the laser beam having
insufficient intensity to melt the metallic layer and a beam
irradiation time ranging from 10 to 200 .mu.s, and including a
plurality of pulses forming a train at intervals of a beam
irradiation pausing time of 15 ms or more. Preferably, the machined
portion is exposed by previously removing, through another
machining method such as etching, the metallic layer positioned at
a target position for laser beam irradiation and in the range
smaller than a shape to be machined. Further, surface roughening
may previously be made to a surface of the metallic layer on a
surface of the wiring board before the laser beam irradiation.
[0029] According to a further aspect of the present invention,
there is provided a laser beam machining method for a wiring board,
including the step of, at a time of pulse irradiation with a laser
beam while sequentially positioning a spot of the laser beam at
target positions on the wiring board in synchronization with a
pulse frequency of the laser beam, providing a time interval of 15
ms or more between two optional successive pulsed laser beams for
irradiation of the respective target positions irrespective of the
pulse frequency by irradiating another target position with a
pulsed laser beam outputted for the time interval therebetween.
[0030] According to a further aspect of the present invention,
there is provided a laser beam machining method for a wiring board,
including the steps of providing a plurality of machining stations
on which the wiring boards to be machined are mounted, sequentially
dividing a pulsed laser beam outputted from a laser oscillator
among the plurality of machining stations for each pulse, and
introducing the pulsed laser beam into the plurality of machining
stations at time intervals of 15 ms or more. Preferably, a carbonic
acid gas laser is used as a light source of the laser beam. The
wiring board may contain glass cloth.
[0031] According to a further aspect of the present invention,
there is provided a laser beam machining apparatus for a wiring
board, including an optical mechanism to change a direction of a
laser beam and move the laser beam on the wiring board while
sequentially positioning a spot of the laser beam at target
positions on the wiring board, and a control mechanism for
synchronous control between a pulse oscillating operation of a
laser oscillator and an operation of the optical mechanism, and
control of the optical mechanism such that a time interval can be
set to 15 ms or more between two optional successive pulsed laser
beams for irradiation of the target positions irrespective of a
pulse frequency of the laser oscillator.
[0032] According to a further aspect of the present invention,
there is provided a laser beam machining apparatus for a wiring
board, including an optical mechanism to sequentially divide a
pulsed laser beam outputted from a laser oscillator among a
plurality of machining stations for each pulse and introduce the
pulsed laser beam into the plurality of machining stations for each
pulse at time intervals of 15 ms or more, and a synchronization
control mechanism for synchronous control between a dividing
operation of the optical mechanism and a pulse oscillating
operation of the laser oscillator. Preferably, the optical
mechanism is provided with at least one rotary chopper rotated at a
predetermined speed of rotation, having a plurality of reflection
surfaces and a plurality of passing portions at positions equally
dividing a periphery about an axis in a plane perpendicular to the
rotation axis. Further, the synchronization control mechanism is
provided with a trigger generating apparatus to generate a trigger
each time all the equally divided areas including the plurality of
reflection surfaces and the plurality of passing portions in the
rotary chopper respectively move across an optical axis of the
laser beam.
[0033] According to a further aspect of the present invention,
there is provided a carbonic acid gas laser oscillator for
machining a wiring board, in which a length of a discharge space in
a gas flow direction is equal to or more than a width of an
aperture, an optical axis passing through a center of the aperture
is set to be positioned in the range that an entire area of the
aperture does not extend off an area extending in the gas flow
direction of the discharge space and on the farthest upstream side
of the gas flow, and a rise time and a fall time are set to 50
.mu.s or less in discharge power fed to the discharge space.
[0034] The above and further objects and novel features of the
invention will more fully appear from the following detailed
description when the same is read in connection with the
accompanying drawings. It is to be expressly understood, however,
that the drawings are for purpose of illustration only and are not
intended as a definition of the limits of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a typical diagram illustrating a laser beam
machining method for a wiring board according to the embodiment 1
of the present invention;
[0036] FIG. 2 is a graph diagram showing a relationship between
energy density of a laser beam and a machining depth of a glass
epoxy material in the laser beam machining method for the wiring
board according to the embodiment 1 of the present invention;
[0037] FIG. 3 is a graph diagram showing a variation in amount of
projection of glass cloth at a machined portion and a variation in
rate of damage to copper foil when a pulse width is varied in the
laser beam machining method for the wiring board according to the
embodiment 1 of the present invention;
[0038] FIG. 4 is a typical diagram showing a laser beam machining
method for a wiring board according to the embodiment 2 of the
present invention;
[0039] FIG. 5 is a waveform diagram showing an irradiation pattern
of a laser beam in the laser beam machining method for the wiring
board according to the embodiment 2 of the present invention;
[0040] FIG. 6 is a graph diagram showing a variation in thickness
of a char layer observed on the rear side of a machined hole
immediately after machining when a beam irradiation pausing time is
varied in the laser beam machining method for the wiring board
according to the embodiment 2 of the present invention;
[0041] FIG. 7 is a machined portion temperature characteristic
diagram showing a relationship between a distance from a surface of
the machined portion and a temperature by using the beam
irradiation pausing time as a parameter;
[0042] FIG. 8 is a waveform diagram showing an irradiation pattern
of a laser beam in the embodiment 3 of the present invention;
[0043] FIG. 9 is a graph diagram showing a variation in thickness
of a char layer when a beam irradiation pausing time is varied
between pulses among pulse groups in a laser beam machining method
for a wiring board according to the embodiment 3 of the present
invention;
[0044] FIG. 10 is a graph diagram showing a variation in thickness
of a char layer when a pulse group interval beam irradiation
pausing time is varied in the laser beam machining method for the
wiring board according to the embodiment 3 of the present
invention;
[0045] FIG. 11 is a graph diagram showing a variation in machining
time required for drilling when the number of pulses among the
pulse groups is varied in the laser beam machining method for the
wiring board according to the embodiment 3 of the present
invention;
[0046] FIG. 12 is a typical diagram illustrating a laser beam
machining method for a wiring board according to the embodiment 4
of the present invention;
[0047] FIG. 13 is an explanatory view showing an existence region
of a copper foil removed portion and a scanning path for raster
scanning in the laser beam machining method for the wiring board
according to the embodiment 4 of the present invention;
[0048] FIG. 14 is a graph diagram showing a variation in amount of
projection of glass cloth at a machined portion when a scanning
speed of a laser beam is varied in the laser beam machining method
for the wiring board according to the embodiment 4 of the present
invention;
[0049] FIG. 15 is a typical diagram illustrating a laser beam
machining method for a wiring board according to the embodiment 5
of the present invention;
[0050] FIG. 16(a) is an explanatory view showing a superimposed
portion beam irradiated portions in case of square beam scanning in
the laser beam machining method for the wiring board according to
the embodiment 5 of the present invention;
[0051] FIG. 16(b) is an explanatory view showing a superimposed
portion of beam irradiated portions in case of circular beam
scanning;
[0052] FIG. 17 is a typical diagram illustrating a laser beam
machining method for a wiring board according to the embodiment 6
of the present invention;
[0053] FIG. 18 is a typical diagram illustrating a laser beam
machining method for a wiring board according to the embodiment 7
of the present invention;
[0054] FIG. 19(a) is a plan view showing a machined shape of a
copper foil removed portion in the laser beam machining method for
the wiring board according to the embodiment 7 of the present
invention;
[0055] FIG. 19(b) is a plan view showing a machined shape of a
copper foil removed portion in which copper foil is removed over an
entire machined portion;
[0056] FIG. 20 is a typical diagram illustrating a laser beam
machining method for a wiring board according to the embodiment 8
of the present invention;
[0057] FIG. 21 is an explanatory view showing a direction of raster
scanning by a laser beam, and a gas flow spraying direction in the
laser beam machining method for the wiring board according to the
embodiment 8 of the present invention;
[0058] FIG. 22 is a typical diagram illustrating a laser beam
machining method for a wiring board according to the embodiment 9
of the present invention;
[0059] FIG. 23 is a typical diagram showing the result of machining
of a printed board according to the embodiment 9 of the present
invention;
[0060] FIG. 24 is a typical diagram showing a laser beam machining
method for a wiring board according to the embodiment 10 of the
present invention;
[0061] FIG. 25 is a typical diagram showing a laser beam machining
method for a wiring board according to one modification of the
embodiment 10 of the present invention;
[0062] FIG. 26 is a typical diagram showing a laser beam machining
method for a wiring board, and a laser beam machining apparatus for
a wiring board according to the embodiment 11 of the present
invention;
[0063] FIG. 27 is a typical diagram showing a laser beam machining
method for a wiring board, and a laser beam machining apparatus for
a wiring board according to the embodiment 12 of the present
invention;
[0064] FIG. 28 is a typical diagram of a rotary chopper according
to the embodiment 12 of the present invention;
[0065] FIG. 29 is a time chart of a trigger and laser pulses in the
embodiment 12 of the present invention;
[0066] FIG. 30 is a perspective view of a carbonic acid gas laser
oscillator for machining a wiring board according to the embodiment
13 of the present invention;
[0067] FIGS. 31(a) and 31(b) are typical diagrams respectively
showing a gain distribution and arrangement of an optical axis in a
discharge space in a conventional carbonic acid gas laser
oscillator;
[0068] FIG. 32 is a typical diagram showing arrangement of an
optical axis in the carbonic acid gas laser oscillator for
machining the wiring board according to the embodiment 13 of the
present invention;
[0069] FIG. 33 is a sectional view showing a structure of a
conventional multi-layer printed board;
[0070] FIG. 34 is a graph diagram showing a mechanism to generate a
reduction in quality in a conventional laser beam machining method
for a wiring board;
[0071] FIG. 35 is a sectional view of a machined portion, showing
projection of glass cloth and a thickness of a char layer in the
conventional laser beam machining method for the wiring board;
and
[0072] FIG. 36 is a sectional view of a machined portion, showing
damage to copper foil in the conventional laser beam machining
method for the wiring board.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0073] A description will now be given of preferred embodiments of
the present invention.
Embodiment 1
[0074] FIG. 1 is a typical diagram showing a laser beam machining
method for a wiring board according to the embodiment 1 of the
present invention. In the drawing, reference numeral 1A means a
printed board (wiring board), 2, 3, and 4 are conductor layers
(metallic layers) including copper foil, 8 is a copper foil removed
portion formed in the top conductor layer 2 by etching, 9 is a ZnSe
lens for convergence of a laser beam 27 radiated from a carbonic
acid gas laser, and 10 is an assist gas for lens protection. Air is
employed in the embodiment as the assist gas 10. Reference numerals
11 and 12 are insulating base materials, and 19 is a gas nozzle
through which the assist gas 10 is ejected. Here, the copper foil
removed portion 8 is formed in the conductor layer 2 at a portion
corresponding to a machined portion of the insulating base material
11.
[0075] In the embodiment 1, a three-layer glass epoxy printed board
(FR-4) with both sides coated with copper foil and a thickness of
200 .mu.m is used as the multi-layer printed board 1A. Further, the
copper foil has a thickness of 18 .mu.m in the conductor layers 2,
3, and 4, and the copper foil removed portion 8 with a diameter of
200 .mu.m is formed in the top conductor layer 2 by the
etching.
[0076] A description will now be given of the operation.
[0077] FIG. 2 is a graph diagram showing the result of machining in
which the carbonic acid gas laser is used as a light source, and
energy per pulse is varied in the laser beam 27 therefrom, thereby
varying energy density in the range from 7 to 35 J/cm.sup.2 at the
copper foil removed portion 8 corresponding to the machined portion
of the printed board 1A, and irradiating an exposed portion of the
insulating base material 11 with only one pulse through the copper
foil removed portion 8. In the graph, the transverse axis defines
energy density (J/cm.sup.2), and the ordinate axis defines a
machining depth (.mu.m) of a glass epoxy material. As is apparent
from FIG. 2, a variation in energy density per pulse of the laser
beam 27 varies the machining depth of the printed board 1A made of
the glass epoxy material. If the energy density is 20 J/cm.sup.2 or
less, machining is carried out with a negligible amount of removal.
Thus, it is necessary to irradiate with a lot of pulses so as to
pass through the glass epoxy material with a thickness of 100
.mu.m. In view of productivity, a through-hole should be formed by
several pulses per hole. Therefore, from the result of experiment
shown in FIG. 2, it can be seen that high-speed and efficient
machining requires irradiation with the laser beam 27 with the
energy density of 20 J/cm.sup.2 or more.
[0078] FIG. 3 is a graph diagram showing the result of machining in
which the laser beam 27 per pulse has constant energy density of
200 mJ, the laser beam 27 is condensed through the ZnSe lens 9 so
as to provide a beam diameter of 500 .mu.m on a surface of the
machined portion of the printed board 1A, and set energy density to
100 J/cm.sup.2, and the copper foil removed portion 8 is irradiated
with only one pulse with a pulse width varying in the range of 1 to
500 .mu.s. In the drawing, the transverse axis defines the pulse
width (.mu.s), and the ordinate axes define an amount of projection
(.mu.m) of glass cloth and a ratio (%) of damage to the copper
foil. In this case, the air was used as the assist gas 10 for lens
protection, and was supplied to the machined portion through the
gas nozzle 19 at a flow rate of 10 l/min.
[0079] It is possible to check the amount of projection of the
glass cloth in a machined hole (or the base material removed
portion) at a time of varying the pulse width of the laser beam 27,
by observing a section of the machined hole through a microscope as
shown in FIG. 35. In FIG. 3, variations in maximum value of the
amount of projection of the glass cloth and in ratio of damage to
the copper foil are plotted versus a variation in pulse width
ranging from 1 to 500 .mu.s. The ratio of damage to the copper foil
is expressed as a percentage by using the number of machined holes
passing through the conductor layer 3 serving as the bottom copper
foil among 1,000 machined holes. As shown in FIG. 3, when the pulse
width of the laser beam 27 is set in the range from 10 to 200
.mu.s, it is possible to provide a machined hole with a little
amount of projection of the glass cloth, and no damage to the
bottom copper foil. In such a manner, by setting a beam irradiation
time to 200 .mu.s or less, it is possible to provide a sharp
temperature gradient of a machined portion during machining
(hereinafter, the machined portion as used herein meaning, for
example, the machined hole during or after the machining) in the
printed board 1A in the range from a surface of the machined
portion to an inside portion. Further, it is possible to reduce the
amount of projection of the glass cloth to a substantially
negligible extent. In addition, since an amount of generating
carbides is reduced, the damage to the copper foil can be reduced,
and a blind via hole can stably be formed.
[0080] After ultrasonic cleaning and desmearing of the obtained
machined hole, the machined hole was plated with copper, and a
pattern was formed, thereafter observing the section of the hole.
It came clear that plasma was caused at the machined portion during
the laser beam machining when the laser beam 27 had a pulse width
less than 10 .mu.s, and the glass cloth was not completely removed
due to the plasma. As a result, the bottom copper foil was not
completely conductive in spite of the plating so that the many
machined holes could not serve as a through-hole. On the other
hand, when the laser beam 27 had a pulse width in the range from 10
to 200 .mu.s, it was possible to provide a good through-hole in
which all copper foil including the bottom copper foil were
completely conductive through the plating. For comparison, though
the same machining was carried out by using a diamond drill with a
diameter of 200 .mu.m, it was difficult to control a depth. That
is, 10% of the 1,000 machined holes passed through the conductor
layer 4 serving as bottom copper foil so that the conductor layer 3
and the conductor layer 4 were short-circuited. As described above,
through the drill machining, it was difficult to provide an effect
identical with that achieved by the laser beam machining method for
the wiring board according to the embodiment 1.
[0081] As set forth above, according to the embodiment 1, at a time
of irradiating the machined portion with the laser beam 27 having
energy density of 20 J/cm.sup.2 or more required for efficient
machining of the printed board 1A made of the glass epoxy material
containing the glass cloth and the epoxy resin, the beam
irradiation time is appropriately set in the range from 10 to 200
.mu.s. Since it is thereby possible to reduce power density to
2.times.10.sup.6 W/cm.sup.2 or less, the machining can be carried
out without the plasma generating at the machined portion. Further,
by setting the beam irradiation time to 200 .mu.s or less, it is
possible to provide the sharp temperature gradient of the machined
portion during machining in the printed board 1A in the range from
the surface of the machined portion to the inside portion. Further,
it is possible to reduce the amount of projection of the glass
cloth to the substantially negligible extent. In addition, since
the amount of generating carbides can be reduced, the damage to the
copper foil can be reduced, and the blind via hole can stably be
formed.
Embodiment 2
[0082] FIG. 4 is a typical diagram showing a laser beam machining
method for a wiring board according to the embodiment 2 of the
present invention. In the drawing, the same reference numerals are
used for component parts identical with those in FIG. 1, and
descriptions thereof are omitted. Further, in FIG. 4, reference
numeral 1B means a multi-layer printed board, 5 is a conductor
layer, 6 is a conductor layer on a rear surface of the multi-layer
printed board 1B, 7 is metal deposited on an inner surface of a
through-hole 17, and 13 and 14 are insulating base materials. FIG.
5 is a waveform diagram showing an irradiation pattern of a laser
beam 27 in the embodiment 2.
[0083] In the embodiment 2, a five-layer glass polyimide board with
a thickness of 400 .mu.m was used as the printed board 1B. In a top
conductor layer 2 and a bottom conductor layer 6, copper foil had a
thickness of 18 .mu.m, and etching was made to form copper foil
removed portions 8 with a diameter of 200 .mu.m in the conductor
layer 2 and the conductor layer 6 at positions corresponding to a
conduction hole to be machined.
[0084] A description will now be given of the operation.
[0085] A carbonic acid gas laser with a pulse width of 50 .mu.s and
pulse energy of 280 mJ was condensed on the printed board 1B
through a ZnSe lens 9 such that a laser beam diameter became 500
.mu.m on a surface of the machined portion, thereby setting energy
density to 143 J/cm.sup.2. Further, a beam irradiation pausing time
shown in FIG. 5 was varied in the range from 12.5 to 50 ms, and a
portion of the insulating base material 11 exposed through the
copper foil removed portion 8 was irradiated with the pulsed laser
beam 27. At the time, air was used as an assist gas 10 for lens
protection, and was supplied to the machined portion through a gas
nozzle 19 at a flow rate of 10 l/min. FIG. 6 is a graph diagram
showing a variation in thickness (.mu.m) of a char layer observed
on the rear side of the machined hole immediately after the
machining when the beam irradiation pausing time is varied as
described above. It is possible to check the thickness of the char
layer by observing a section of the machined hole through a
microscope as shown in FIG. 35.
[0086] As shown in FIG. 6, when the beam irradiation pausing time
is below 15 ms, the thickness of the char layer rapidly increases.
After the laser beam machining, the obtained printed board 1B was
ultrasonically cleaned by pure water for three minutes. It was
thereby possible to completely remove the char layer in case of the
beam irradiation pausing time of 15 ms or more. After the
ultrasonic cleaning and desmearing of the obtained machined hole,
the machined hole was plated with copper, and a pattern was formed,
thereafter observing the section. It was possible to provide a good
through-hole having a diameter of 200 .mu.m and a smooth inner wall
in case of the beam irradiation pausing time of 15 ms or more. On
the other hand, in case of the beam irradiation pausing time less
than 15 ms, a residual char layer and projecting glass cloth were
observed between a metallic deposit and a base material of the
printed board 1B, the hole had a rough inner wall, and throwing
power in plating was insufficient.
[0087] It can be considered that, as shown in FIG. 7, the above
problems were caused because, in case of the beam irradiation
pausing time less than 15 ms, a gradual temperature gradient was
provided by machining according to a distance from a surface of the
machined portion during the machining, and a temperature was
excessively increased at a deep portion from the surface of the
machined portion, at which a rise of the temperature was
unnecessary. On the other hand, if the same beam irradiated portion
is irradiated with the pulsed laser beam 27 with the beam
irradiation pausing time of 15 ms or more, it is possible to ensure
a cooling time required to completely cool the machined portion for
each pulse. As shown in FIG. 7, in case of the beam irradiation
pausing time of 15 ms or more, it is possible to reduce gradation
of the temperature gradient caused due to the temperature rise at
the machined portion during irradiation with the laser beam 27, and
reduce the projection of the glass cloth.
[0088] As set forth above, the carbonic acid gas laser is used for
multi-pulse irradiation at appropriate irradiation intervals. It is
thereby possible to provide the conduction hole having a high
aspect ratio which can not be obtained by a single pulse, and
rapidly machine the printed board including the glass cloth with
high accuracy.
[0089] For comparison, though the same machining was carried out by
using a diamond drill with a diameter of 200 .mu.m, the drill was
worn out after machining for about 1,000 machined holes, resulting
in the rough inner wall of the hole and occasional breakage of the
drill. Hence, the method required a machining time about ten times
a machining time in the laser beam machining method for the wiring
board according to the embodiment 2.
[0090] As set forth above, according to the embodiment 2, since the
same beam irradiated portion is irradiated with the pulsed laser
beam at intervals of the beam irradiation pausing time of 15 ms or
more, it is possible to ensure the cooling time required to
completely cool the machined portion for each pulse. As shown in
FIG. 7, it is possible to increase the temperature gradient of the
machined portion, and reduce heating at the machined portion. As a
result, it is possible to reduce the projection of the glass cloth,
and rapidly machine the printed board containing the glass cloth
with high accuracy even in case of multi-pulse irradiation.
Embodiment 3
[0091] FIG. 8 is a waveform diagram showing an irradiation pattern
of a laser beam in a laser beam machining method for a wiring board
according to the embodiment 3 of the present invention. In the
embodiment 3, as shown in FIG. 4 of the embodiment 2, a five-layer
glass polyimide board with a thickness of 400 .mu.m was used as a
printed board 1B. In a top conductor layer 2 and a bottom conductor
layer 6, copper foil had a thickness of 18 .mu.m, and etching was
made to form copper foil removed portions 8 with a diameter of 200
.mu.m in the conductor layer 2 and the conductor layer 6 at
positions corresponding to a conduction hole to be machined.
[0092] A description will now be given of the operation.
[0093] A laser beam 27 was emitted from a carbonic acid gas laser
with a constant pulse width of 50 .mu.s, and constant pulse energy
of 280 mJ. Further, the laser beam 27 was condensed on the printed
board 1B through a ZnSe lens 9 such that a laser beam diameter
became 500 .mu.m on a surface of the machined portion, thereby
setting energy density to 143 J/cm.sup.2. As shown in FIG. 8, there
were provided a plurality of pulse groups respectively including
two to ten pulses with a beam irradiation pausing time of t1, and
the printed board 1B was irradiated with the pulse groups for a
pulse group interval beam irradiation pausing time of t2.
[0094] In the embodiment, the beam irradiation pausing time t1 was
varied in the range from 0 to 10 ms, and the pulse group interval
beam irradiation pausing time t2 was varied in the range from 50 to
10 ms. A portion of an insulating base material 11 exposed through
the copper foil removed portion 8 was irradiated with 52 pulses. At
the time, air was used as an assist gas 10 for lens protection, and
was supplied to the machined portion through a gas nozzle 19 at a
flow rate of 10 l/min.
[0095] FIG. 9 is a graph diagram showing a variation in thickness
of a char layer observed on the rear side of a machined hole
immediately after the machining when the beam irradiation pausing
time t1 was varied between pulses among the pulse groups. In this
case, the pulse group interval beam irradiation pausing time t2 was
set to a sufficiently large value of 50 ms. As shown in FIG. 9,
when the beam irradiation pausing time t1 was equal to or more than
4 ms, the thickness of the char layer became thinner than a
thickness (ranging from 50 to about 100 .mu.m) of the layer in case
of the beam irradiation pausing time t1 of 0 ms. Thus, it can be
seen that the variation in beam irradiation pausing time t1 can
effectively reduce the thickness of the char layer.
[0096] FIG. 10 is a graph diagram showing a variation in thickness
of a char layer observed on the rear side of a machined hole
immediately after the machining when the pulse group interval beam
irradiation pausing time t2 was varied from 50 to 10 ms. In this
case, the number of pulses among the pulse groups was set to two,
and the beam irradiation pausing time t1 was set to 10 ms. As shown
in FIG. 10, when the pulse group interval beam irradiation pausing
time t2 was 20 ms or less, the thickness of the char layer rapidly
increased.
[0097] FIG. 11 is a graph diagram showing a variation in thickness
of a char layer observed on the rear side of a machined hole
immediately after the machining with respect to a variation in
machining time required for drilling when the number of pulses
among the pulse groups was varied. At the time, the beam
irradiation pausing interval t1 between the pulses was set to 25
ms, and the pulse group interval beam irradiation pausing time t2
was set to 50 ms. As shown in FIG. 11, when the number of pulses is
4 or less, with the same machining quality, it is possible to
reduce about 6 to 22% of a machining time required for machining by
a single pulse frequency.
[0098] After ultrasonic cleaning and desmearing of the obtained
machined hole, the machined hole was plated with copper, and a
pattern was formed, thereafter observing a section. When the beam
irradiation pausing time t1 between pulses was 4 ms or more, the
pulse group interval beam irradiation pausing time t2 was 20 ms or
more, and the number of pulses in the pulse groups was 4 or less,
it was possible to provide a good through-hole having a diameter of
200 .mu.m and a smooth inner wall as in the case of the single
pulse frequency. Further, in case of a thin-walled printed board,
it was possible to provide a good through-hole even when the number
of pulses among the pulse groups was 4 or more with satisfaction of
the above conditions of the beam irradiation pausing time t1 and
the pulse group interval beam irradiation pausing time t2. That is,
it was possible to reduce the machining time by satisfying the
conditions of the beam irradiation pausing time t1 and the pulse
group interval beam irradiation pausing time t2 so as to
appropriately select the number of pulses among the pulse groups
according to a thickness of the printed board. Further, if the
conditions of the beam irradiation pausing time t1 and the pulse
group interval beam irradiation pausing time t2 were not met, a
residual char layer and projecting glass cloth were observed
between a metallic deposit and a base material of the printed board
1B, the hole had a rough inner wall, and throwing power in plating
was insufficient.
[0099] As set forth above, according to the embodiment 3, the
appropriate beam irradiation pausing time is provided, and the
multi-pulse irradiation is carried out with the pulse groups
including the several pulses. It is thereby possible to reduce the
machining time to be less than that in case of the single pulse. At
the same beam irradiated portion, the machined portion is
irradiated with the pulsed laser beam having the plurality of pulse
groups respectively including the plurality of pulses with
intervals of the predetermined beam irradiation pausing time with
intervals of the pulse group interval beam irradiation pausing time
longer than the beam irradiation pausing time between the pulses.
It is thereby possible to prevent a rise of a temperature at the
machined portion, reduce gradation of the temperature gradient with
respect to a depth distance from the surface of the machined
portion, and reduce the projection of the glass cloth.
Embodiment 4
[0100] FIG. 12 is a typical diagram illustrating a laser beam
machining method for a wiring board according to the embodiment 4
of the present invention. In the drawing, the same reference
numerals are used for component parts identical with or equivalent
to those in FIG. 1, and descriptions thereof are omitted. In the
embodiment, a three-layer glass epoxy printed board (FR-4) with a
thickness of 500 .mu.m was used as a multi-layer printed board 1C.
Further, copper foil had a thickness of 18 .mu.m in conductor
layers 2, 3, and 4, a distance between the conductor layer 2 and
the conductor layer 3 was 200 .mu.m, and a copper foil removed
portion 8 with a diameter of 200 .mu.m was formed in the top
conductor layer 2 by etching.
[0101] A description will now be given of the operation.
[0102] A laser beam 27 was emitted from a carbonic acid gas laser
with constant pulse energy of 280 mJ, a constant pulse width of 50
.mu.s and a constant pulse frequency of 400 Hz. Further, the laser
beam 27 was condensed on the printed board 1C through a ZnSe lens 9
such that a laser beam diameter became 1 mm on a surface of a
machined portion, thereby setting energy density to 35 J/cm.sup.2.
As shown in FIG. 13, a raster scanning was made on a path 26 with a
scanning speed ranging from 8 to 3 m/min and a scanning pitch of
100 .mu.m such that an entire existence region 25 of the copper
foil removed portion 8 was irradiated with the laser beam 27. At
the time, air was used as an assist gas 10 for lens protection, and
was supplied to the machined portion through a gas nozzle 19 at a
flow rate of 10 l/min.
[0103] FIG. 14 is a graph diagram showing a variation in amount of
projection of glass cloth in a machined hole when the scanning
speed of the laser beam 27 is varied. In the drawing, as the amount
of projection of the glass cloth, the maximum value thereof is
plotted. As shown in FIG. 14, when the scanning speed of the laser
beam 27 is in the range of 8 to 6 m/min, it is possible to provide
a machined hole with a small amount of projection of the glass
cloth and no damage to bottom copper foil.
[0104] After ultrasonic cleaning and desmearing of the obtained
machined hole, the machined hole was plated with copper, and a
pattern was formed, thereafter observing a section. When the
scanning speed of the laser beam 27 was 6 m/min or less, the amount
of projection of the glass cloth became 20 .mu.m or more due to
heat, resulting in insufficient throwing power. As a result, there
were observed many printed boards having plating solution soaking
into the glass cloth. On the other hand, when the scanning speed of
the laser beam 27 was in the range from 8 to 6 m/min, it was
possible to highly efficiently provide a good conduction hole in
which all the copper foil including the bottom copper foil were
completely conductive through the plating.
[0105] As set forth above, according to the embodiment 4, it is
possible to tremendously increase a machining speed while keeping
the same machining quality as that of the same machining by
positioning the laser beam 27 for each machined portion. Further,
it is possible to reduce, for example, the projection of the glass
cloth during the machining of the printed board, thereby enabling
high quality machining such as drilling of a through-hole and a
blind via hole, grooving, and cutting for an outside shape.
Embodiment 5
[0106] FIG. 15 is a typical diagram illustrating a laser beam
machining method for a wiring board according to the embodiment 5
of the present invention. In the drawing, the same reference
numerals are used for component parts identical with those in FIG.
1, and descriptions thereof are omitted. Reference numeral 48 means
a beam shaping optical system to shape a laser beam 27 through a
kaleidoscope such that the laser beam 27 can have a beam spot size
of 0.9 mm.times.0.9 mm on a surface of a machined portion.
[0107] In the embodiment 5, as in the embodiment 4, a three-layer
glass epoxy printed board (FR-4) with a thickness of 500 .mu.m was
used as a printed board 1C. Further, copper foil had a thickness of
18 .mu.m in conductor layers 2, 3, and 4, a distance between the
conductor layer 2 and the conductor layer 3 was 200 .mu.m, and a
copper foil removed portion 8 with a diameter of 200 .mu.m was
formed in the top conductor layer 2 by etching.
[0108] A description will now be given of the operation.
[0109] A laser beam 27 was emitted from a carbonic acid gas laser
with constant pulse energy of 280 mJ, a constant pulse width of 50
.mu.s and a constant pulse frequency of 800 Hz. Further, the laser
beam 27 was condensed on the multi-layer printed board 1C through a
ZnSe lens 9 after shaping by using the beam shaping optical system
48 including the kaleidoscope such that the laser beam 27 had the
beam spot size of 0.9 mm.times.0.9 mm on the surface of the
machined portion, thereby setting energy density to 35 J/cm.sup.2.
As in the embodiment 4, a raster scanning was made with a scanning
speed of 6 m/min and a scanning pitch of 200 .mu.m such that an
entire existence region of the copper foil removed portion 8 was
irradiated with the laser beam 27. At the time, air was used as an
assist gas 10 for lens protection, and was supplied to the machined
portion through a gas nozzle 19 at a flow rate of 10 l/min.
Further, for comparison, the same laser beam machining was made by
a circular beam with the same energy density and a diameter of 1
mm.
[0110] As a result, as shown in FIG. 16(a), when a path 26 is
scanned by a square laser beam 27a having a square laser beam on a
machined portion 21, it was possible to provide a machined hole
with a small amount of projection of glass cloth and no damage to
bottom copper foil. On the other hand, as shown in FIG. 16(b), in
case of a circular laser beam 27b, there were caused carbonization
in the machined hole and breakage of the bottom copper foil.
[0111] This is because, as shown in FIGS. 16(a) and 16(b), a
superimposed portion 24 of beam irradiated portions can more be
reduced in scanning by the square laser beam 27a having the square
laser beam on the machined portion 21 of the printed board 1C than
would be in scanning by the circular laser beam 27b. As a result,
the square laser beam 27a can decrease gradation of a temperature
gradient generated according to a temperature rise at the machined
portion, and can more reduce a lower limit of a beam irradiation
pausing time than would be in the circular laser beam 27b. By
scanning the surface of the printed board 1C by the pulse carbonic
acid gas laser, it is possible to carry out the machining of the
printed board 1C such as drilling for a through-hole and a blind
via hole, grooving, and cutting for an outside shape at a more
rapid machining speed than that in case of the circular laser beam
27b, resulting in the same machining quality.
[0112] After ultrasonic cleaning and desmearing of the obtained
machined hole, the machined hole was plated with copper, and a
pattern was formed, thereafter observing a section. In case of the
circular laser beam 27b, the amount of projection of the glass
cloth became 20 .mu.m or more due to heat, resulting in
insufficient throwing power. As a result, there were observed many
printed boards having plating solution soaking into the glass
cloth. On the other hand, in case of the square laser beam 27a, it
was possible to provide a good conduction hole in which all the
copper foil including the bottom copper foil were completely
conductive through the plating.
[0113] As set forth above, according to the embodiment 5, the
square laser beam is provided on the surface of the sample. It is
thereby possible to provide a more rapid machining speed than that
in case of the circular laser beam 27b while keeping good machining
quality.
Embodiment 6
[0114] FIG. 17 is a typical diagram illustrating a laser beam
machining method for a wiring board according to the embodiment 6
of the present invention. In the drawing, the same reference
numerals are used for component parts identical with those in FIG.
1, and descriptions thereof are omitted. Reference numeral 1D means
a printed board, and a glass epoxy printed board (FR-4) with a
thickness of 200 .mu.m and both sides coated with copper is used as
the printed board 1D. Copper foil has a thickness of 18 .mu.m in
conductor layers 2 and 3. Etching with a pitch of 10 mm is made to
remove copper foil with a width of 1 mm and a length of 10 mm so as
to form copper foil removed portions 8 in the top conductor layer 2
and the bottom conductor layer 3 in the printed board 1D at the
same position.
[0115] A description will now be given of the operation.
[0116] According to the embodiment 6, a laser beam 27 was emitted
from a carbonic acid gas laser with constant pulse energy of 280
mJ, a constant pulse width of 50 .mu.s and a constant pulse
frequency of 400 Hz. Further, the laser beam 27 was condensed on
the printed board 1D through a ZnSe lens 9 such that the laser beam
27 had a beam diameter of 1 mm on a surface of a machined portion,
thereby setting energy density to 35 J/cm.sup.2. As shown in FIG.
13, a raster scanning was made with a scanning pitch of 100 .mu.m
and a scanning speed of 8 m/min such that an entire existence
region 25 of the copper foil removed portion 8 was irradiated with
the laser beam 27. At the time, air was used as an assist gas 10
for protection of the ZnSe lens 9, and was supplied to the machined
portion through a gas nozzle 19 at a flow rate of 10 l/min. Though
no glass cloth projected and no char layer was generated, there
were rigid residual additionally deposited around the machined hole
due to large volumes of removed base materials.
[0117] After the machining, the laser beam 27 was emitted from the
carbonic acid gas laser with the constant pulse energy of 200 mJ,
the constant pulse width of 50 .mu.s and the constant pulse
frequency of 400 Hz. Further, the laser beam 27 was condensed on
the printed board 1D through the ZnSe lens 9 such that the laser
beam 27 had the beam diameter of 1 mm on the surface of the
machined portion, thereby setting the energy density to 25
J/cm.sup.2. As in the above machining, a second raster scanning was
made with a scanning speed of 10 m/min and a scanning pitch of 100
.mu.m such that an entire existence region 25 of the copper foil
removed portions 8 was irradiated with the laser beam 27. At the
time, air was used as the assist gas 10 for protection of the ZnSe
lens 9, and was supplied to the machined portion through the gas
nozzle 19 at the flow rate of 10 l/min. This can substantially
completely remove the additional deposits around the machined hole
without damage to the top copper foil.
[0118] After ultrasonic cleaning and desmearing of the obtained
machined hole, the machined hole was plated with copper, and a
pattern was formed, thereafter observing a section. It was possible
to provide a good slit which was completely conductive through the
plating without the residual additional deposit around the machined
hole.
[0119] As set forth above, according to the embodiment 6, after the
base material is removed by beam irradiation, the machined hole and
a periphery of the machined hole, or only the periphery of the
machined hole is irradiated with the laser beam 27 once again to
remove soot additionally deposited around the machined hole. The
second beam irradiation is used to remove only the soot, resulting
in a small amount of removal and no additionally deposited soot.
Thereby, even when a portion to be machined is larger than the
laser beam diameter, for example, even in case of cutting,
grooving, or drilling for a large diameter hole, it is possible to
remove the additional deposits without the step for complicated
after-treatment such as wet etching to remove the additionally
deposited soot serving as the residual in the machined hole after
the machining. As a result, it is possible to avoid a reduction in
reliability of insulation and reliability of metallic deposit in
the printed board.
Embodiment 7
[0120] FIG. 18 is a typical diagram illustrating a laser beam
machining method for a wiring board according to the embodiment 7
of the present invention. In the drawing, the same reference
numerals are used for component parts identical with those in FIG.
1, and descriptions thereof are omitted. Reference numeral 18 means
copper foil removed portions. In the embodiment 7, as in the
embodiment 6, as a printed board 1D was used a glass epoxy printed
board (FR-4) with a thickness of 200 .mu.m and both sides coated
with copper. Further, copper foil had a thickness of 18 .mu.m in
conductor layers 2 and 3. Etching with a pitch of 2 mm was made to
form copper foil removed portions 8 with a width of 1 mm and a
length of 10 mm in the top conductor layer 2 and the bottom
conductor layer 3 on the printed board 1D at the same position. As
shown in FIG. 19(a), the copper foil removed portion 18 was formed
by removing copper foil with a width of 100 .mu.m corresponding to
only an outer periphery 18a of the copper foil removed portion 18
through the etching. Further, for the purpose of confirmation of an
effect in case the copper foil removed portion 18 was used, another
etching was made to entirely remove a portion corresponding to a
machined portion as in the embodiment 6 so as to form a copper foil
removed portion 8 as shown in FIG. 19(b).
[0121] A description will now be given of the operation.
[0122] A laser beam 27 was emitted from a carbonic acid gas laser
with constant pulse energy of 280 mJ, a constant pulse width of 50
.mu.s and a constant pulse frequency of 400 Hz. Further, the laser
beam 27 was condensed on the printed board 1D through a ZnSe lens 9
such that the laser beam 27 had a beam diameter of 1 mm on a
surface of a machined portion, thereby setting energy density to 35
J/cm.sup.2. As in the embodiment 6, a raster scanning was made with
a scanning speed of 8 m/min and a scanning pitch of 100 .mu.m such
that an entire existence region of the copper foil removed portion
18 was irradiated with the laser beam 27. At the time, air was used
as an assist gas 10 for lens protection, and was supplied to the
machined portion through a gas nozzle 19 at a flow rate of 10
l/min.
[0123] As a result, in the printed board in which only the outer
periphery 18a of the copper foil removed portion 18 was machined,
it was possible to form a good slit without projection of glass
cloth, generation of a char layer, and rigid additional deposits on
a periphery of a machined hole. On the other hand, in the printed
board with the copper foil removed portion 8 formed by entirely
removing the portion corresponding to the machined portion as shown
in FIG. 19(b), as described above, no glass cloth projected and no
char layer was generated. However, there were rigid residual
additionally deposited around the machined hole due to large
volumes of removed base materials.
[0124] After ultrasonic cleaning and desmearing of the printed
board 1D obtained by machining only the outer periphery 18a of the
copper foil removed portion 18, the printed board was plated with
copper, and a pattern was formed thereon, thereafter observing a
section. It was possible to provide a good slit which was
completely conductive through the plating without the residual
additional deposit around the machined hole and peeling of the
copper foil.
[0125] As set forth above, according to the embodiment 7, since
only the outer periphery 18a of the copper foil removed portion 18
is machined, a volume of removal can be reduced at a time of
machining so that the machined hole having the same shape can be
provided after the machining. At the time, since a small volume of
machined materials can reduce a temperature rise around the
machined hole, it is possible to reduce gradation of a temperature
gradient as shown in FIG. 7. That is, a larger temperature gradient
can be provided to enable good machining causing no failure such as
peeling of the copper foil even in case of machining with the
removed portion larger than a non-removed portion. Further, a
shorter beam irradiation pausing time can be provided than that in
a method of irradiating the entire machined portion with the beam,
resulting in higher speed machining.
Embodiment 8
[0126] FIG. 20 is a typical diagram illustrating a laser beam
machining method for a wiring board according to the embodiment 8
of the present invention. In the drawing, the same reference
numerals are used for component parts identical with those in FIG.
1, and descriptions thereof are omitted. In the embodiment 8, as in
the embodiment 6, as a printed board 1D serving as a machining
target was used a glass epoxy printed board (FR-4) with a thickness
of 200 .mu.m and both sides coated with copper. Further, copper
foil had a thickness of 18 .mu.m in conductor layers 2 and 3.
Etching with a pitch of 10 mm was made to form copper foil removed
portions 8 with a width of 1 mm and a length of 10 mm in the top
conductor layer 2 and the bottom conductor layer 3 on the printed
board 1D at the same position.
[0127] A description will now be given of the operation.
[0128] A laser beam 27 was emitted from a carbonic acid gas laser
with constant pulse energy of 280 mJ, a constant pulse width of 50
.mu.s and a constant pulse frequency of 400 Hz. Further, the laser
beam 27 was condensed on the printed board 1D through a ZnSe lens 9
such that the laser beam 27 had a beam diameter of 1 mm on a
surface of a machined portion, thereby setting energy density to 35
J/cm.sup.2. As shown in FIG. 21, a raster scanning was made along a
path 26 with a scanning speed of 8 m/min and a scanning pitch of
100 .mu.m such that an entire existence region 25 of the copper
foil removed portion 8 was irradiated with the laser beam 27. At
the time, air was used as an assist gas 10, and was sprayed and
supplied to the machined portion at a flow rate of 50 l/min in a
direction from a machining start portion to a machining end portion
through a gas nozzle 19 moving integrally with the laser beam
27.
[0129] As a result, additional deposits around a machined hole were
blown away by the assist gas, and adhered to only a portion to be
subsequently machined. The additional deposits were removed by the
laser beam 27 at a time of the machining, and a small amount of
additional deposits were finally left at the machining end portion.
The additional deposits were removed by a method identical with the
laser beam machining method for the wiring board described in the
embodiment 6.
[0130] After ultrasonic cleaning and desmearing of the printed
board 1D obtained by the above steps, the printed board was plated
with copper, and a pattern was formed thereon, thereafter observing
a section. It was possible to provide a good slit which was
completely conductive through the plating without the residual
additional deposit around the machined hole.
[0131] As set forth above, according to the embodiment 8, a gas
flow is sprayed onto the currently machined printed board 1D in the
direction from the beam irradiation start portion to the beam
irradiation end portion in the machined portion, thereby blowing
away the removed material to an area to be subsequently irradiated
with the laser beam 27, and depositing the material on a surface
thereof. Since the deposit can be removed concurrently with removal
of the base material, it is possible to reduce the removed material
deposited on a surface of the printed board 1D after the machining,
and reduce the printed board cleaning step after the machining.
Further, it is possible to significantly reduce an area having the
residual additional deposit even in machining with large volumes of
removed materials.
Embodiment 9
[0132] FIG. 22 is a typical diagram illustrating a laser beam
machining method for a wiring board according to the embodiment 9
of the present invention. In the drawing, the same reference
numerals are used for component parts identical with those in FIG.
1, and descriptions thereof are omitted. In the embodiment 9, as a
printed board 1E was used a three-layer glass epoxy printed board
(FR-4) with a thickness of 200 .mu.m and both sides coated with
copper foil. Further, copper foil had a thickness of 18 .mu.m in
conductor layers 2, 3, and 4. The top conductor layer 2 was
provided with no copper foil removed portion formed by etching.
[0133] A description will now be given of the operation.
[0134] A laser beam 27 was emitted from a carbonic acid gas laser
with pulse energy of 400 mJ and a pulse width of 100 .mu.s.
Further, the laser beam 27 was condensed on the printed board 1E
through a ZnSe lens 9 at a just focus position at which the laser
beam 27 had the minimum spot diameter, thereby irradiating with one
pulse. Thereafter, at intervals of a beam irradiation pausing time
of 50 ms, the printed board was irradiated with ten pulses of the
laser beam 27 with pulse energy of 150 mJ and a pulse width of 100
.mu.s. At the time, air was used as an assist gas 10 for lens
protection, and was supplied to a machined portion at a flow rate
of 10 l/min through a gas nozzle 19. In the first irradiated laser
beam 27, pulse energy has sufficient intensity to melt and remove
the top conductor layer 2. In the second and later laser beams 27,
pulse energy has insufficient intensity to melt the top conductor
layer 2.
[0135] FIG. 23 is a typical diagram showing one illustrative result
of machining for the printed board according to the embodiment 9.
In the top conductor layer 2, copper foil including a substantially
complete round with a diameter of 200 .mu.m was removed with little
effect of heat on a periphery. Further, under the conductor layer
2, the machining can be made to form a substantially straight hole
reaching the lowermost copper foil with a small amount of
projection of glass cloth 29. After ultrasonic cleaning and
desmearing of the obtained machined hole, the machined hole was
plated with copper, and a pattern was formed, thereafter observing
a section. It was possible to provide a good through-hole with the
diameter of 200 .mu.m and a smooth inner wall.
[0136] As set forth above, even when the copper foil is not
previously removed in another step such as etching, the machined
portion may be irradiated with the pulsed laser beam 27 from the
carbonic acid gas laser at the just focus position, thereby
increasing the energy density. It is thereby possible to finely
remove the top copper foil with little effect of heat on the
periphery. Thereafter, the printed board may be irradiated a
plurality of times with the laser beam 27 having smaller pulse
energy at intervals of a long beam irradiation pausing time,
resulting in the through-hole with no char layer. It is thereby
possible to omit the etching serving as a previous step which is
essential in the prior art, and simplify manufacturing steps.
Further, both of the above beam irradiation conditions are
identical with those described in, for example, the embodiments 1
and 2. That is, the printed board was irradiated with the pulsed
laser beam 27 for a beam irradiation time ranging from 10 to 200
.mu.s, most suitable for machining of the glass epoxy board, and at
intervals of the beam irradiation pausing time of 15 ms or more.
Therefore, it is possible to provide a sharp temperature gradient
of the machined portion, and provide a platable hole with a
substantially negligible amount of projection of the glass cloth.
As set forth above, even in the printed board having surfaces
coated with the copper foil and containing the glass cloth, it is
possible to rapidly and accurately provide a hole by only the laser
beam machining step without previously removing the conductor layer
such as the copper foil on the surface of the printed board through
the etching, and so forth.
Embodiment 10
[0137] FIG. 24 is a typical diagram showing a laser beam machining
method for a wiring board according to the embodiment 10 of the
present invention. In the drawing, the same reference numerals are
used for component parts identical with those in FIG. 1, and
descriptions thereof are omitted. In the embodiment, as in the
embodiment 9, as a printed board 1E was used a three-layer glass
epoxy printed board (FR-4) with a thickness of 200 .mu.m and both
sides coated with copper foil. Further, copper foil had a thickness
of 18 .mu.m in conductor layers 2, 3, and 4. The top conductor
layer 2 was provided with a finely removed portion 30 in a range
smaller than an area to be machined.
[0138] A description will now be given of the operation.
[0139] A laser beam 27 was emitted from a carbonic acid gas laser
with pulse energy of 200 mJ and a pulse width of 100 .mu.s.
Further, the laser beam 27 was condensed on the printed board 1E
through a ZnSe lens 9 at a just focus position at which the laser
beam 27 had the minimum spot diameter, thereby irradiating with one
pulse. Thereafter, at intervals of a beam irradiation pausing time
of 50 ms, the printed board was irradiated with ten pulses of the
laser beam 27 with pulse energy of 150 mJ and a pulse width of 100
.mu.s. As a result, as in the embodiment 9, in the top conductor
layer 2, copper foil including a substantially complete round with
a diameter of 200 .mu.m was removed with little effect of heat on a
periphery. Further, under the conductor layer 2, the machining can
be made to form a substantially straight hole reaching copper foil
of the lowermost conductor layer 4 with a small amount of
projection of glass cloth.
[0140] Instead of the finely removed portion 30 shown in FIG. 24,
as shown in FIG. 25, surface roughening shown by reference numeral
31 may be made to a surface of the conductor layer 2. The surface
roughening utilizes, for example, chemical treatment typically used
to enhance adhesive properties between a resin layer and a
conductor layer. The surface roughening to the surface of the
conductor layer 2 can improve absorption of the laser beam 27 when
the copper foil having a desired shape is removed from the
conductor layer 2, and enables efficient and more stable
drilling.
[0141] As set forth above, the slight copper foil of a beam
irradiated portion is previously removed by the etching, and the
surface roughening is made to the surface. The treated portions
trigger the absorption of the laser beam 27 from the carbonic acid
gas laser so that the top copper foil can be removed even when the
first irradiated beam has low energy density as in the embodiment
9.
[0142] Alternatively, the two methods according to the embodiment
10 may concurrently be used including one method in which the
slight copper foil of the beam irradiated portion is previously
removed by the etching, and the other method in which the surface
roughening is made to the surface. Alternatively, either one or
both of the methods may be used concurrently with the method in the
embodiment 9. In either case, as in the embodiment 9, the top
copper foil can be removed even when the first irradiated beam has
low energy density.
Embodiment 11
[0143] FIG. 26 is a typical diagram showing a laser beam machining
method for a wiring board, and a laser beam machining apparatus for
a wiring board according to the embodiment 11 of the present
invention. In the drawing, reference numeral 32 means a laser
oscillator, 33 is an f.theta. lens to condense a laser beam 27, 34
is beam scanner apparatus (optical mechanisms) using a galvanometer
scanner, and 35 is a scanner drive/laser trigger apparatus (control
mechanism) to output a drive command for the beam scanner apparatus
34 and a trigger of laser oscillation for the laser oscillator
32.
[0144] A description will now be given of the operation.
[0145] The scanner drive/laser trigger apparatus 35 outputs the
trigger of the laser oscillation for the laser oscillator 32 at a
predetermined pulse frequency, and the drive commands for the two
beam scanner apparatus 34. It is thereby possible to position a
spot of the laser beam 27 at high speed at an optional drilling
position on the printed board 1F having many drilling positions in
synchronization with a pulse frequency of the laser beam 27
radiated from the laser oscillator 32.
[0146] A machining speed per unit time becomes higher as the pulse
frequency becomes higher. However, when irradiation with a
plurality of pulses is required for drilling at one position,
successive irradiation with a high pulse frequency makes a char
layer thicker so that a good hole can not be provided. For example,
as seen from a relationship shown in FIG. 6, the char layer is made
thicker by beam irradiation at intervals of a beam irradiation
pausing time less than 15 ms, that is, at a frequency more than 67
Hz.
[0147] Thus, the spot of the laser beam 27 is sequentially moved to
different drilling positions for each pulse. After all of the many
drilling positions in the range of a scan vision are irradiated
with the laser beam 27 pulse by pulse (after the elapse of a
substantial time of 15 ms or more), or after the elapse of a time
of 15 ms or more from irradiation of the first drilling position
with the laser beam 27, the spot is returned to the first drilling
position. The spot is sequentially moved once again, and the
movement is repeated several times. It is thereby possible to
irradiate one drilling position with the laser beam a plurality of
times while ensuring a beam irradiation pausing time of 15 ms or
more for each drilling position. Therefore, if in synchronization
at a frequency of 200 Hz by using, for example, the beam scanner
apparatus 34 having the galvanometer scanner shown in FIG. 26, a
time of 5 ms is required for each hole. Consequently, when the scan
vision includes three or more drilling positions, and the spot is
sequentially moved toward the positions, the beam irradiation
pausing time of 15 ms or more can be ensured for each drilling
position.
[0148] As set forth above, according to the embodiment 11, even if
the laser beam 27 having a high pulse frequency is used, the beam
irradiation can be made while ensuring the beam irradiation pausing
time of 15 ms or more for each machined portion. It is thereby
possible to provide a high quality platable hole having little char
layer and no projection of glass cloth. Further, a scanning
frequency of the spot of the laser beam 27 can be increased to its
limitation so as to enable high-speed drilling, and drill for many
holes in a short time. Therefore, it is possible to considerably
improve productivity of the printed board containing the glass
cloth.
Embodiment 12
[0149] FIG. 27 is a typical diagram showing a laser beam machining
method for a wiring board, and a laser beam machining apparatus for
a wiring board according to the embodiment 12 of the present
invention. In the drawing, reference numeral 36 means a reflection
mirror disposed across an optical axis of a laser beam 27, and 37
is an XY table on which three printed boards 1F are mounted, for
moving the printed boards in a horizontal plane. That is, the XY
table 37 includes three machining stations. In addition, reference
numeral 38 means a control unit for the XY table 37, 39 is rotary
choppers, 40 is a trigger generating apparatus, 41 is a trigger
counting portion, and ST1 to ST3 are one pulses of the laser beam
27. The laser beam machining method for the wiring board according
to the embodiment 12 is used for concurrent machining of the
plurality of printed boards 1F. The embodiment will be described by
way of a method for the concurrent machining of the three printed
boards 1F as one example. In the embodiment, an optical mechanism
includes the rotary choppers 39 and the reflection mirror 38, and a
synchronization control mechanism includes the trigger generating
apparatus 40 and the trigger counting portion 41.
[0150] A description will now be given of the operation.
[0151] As shown in FIG. 28, in the rotary chopper 39, a disk
mounted perpendicular to a rotation axis is equally divided into
(3.times.n) areas (n=1, 2, 3, . . . ), and the equally divided
areas are repeatedly mounted in the order of a reflection surface
39a, a passing portion 39b, and a passing portion 39b in a
direction of rotation. In FIG. 28, the rotary chopper 39 is a
cross-shaped reflector obtained by equally dividing a disk into
(3.times.4) areas to have the four reflection surfaces 39a.
[0152] As shown in FIG. 27, the two rotary choppers 39 are mounted
between the laser oscillator 32 and the reflection mirror 36, and
are set to rotate, with a deviation by one of the equally divided
areas, in synchronization with each other at the same speed. Any
one of the rotary choppers 39 is provided with the trigger
generating apparatus 40 to output the trigger to the trigger
counting portion 41 each time the (3.times.n) equally divided areas
respectively move across the optical axis of the laser beam 27. The
trigger generating apparatus 40 sends the generating trigger to the
trigger counting portion 41. The trigger counting portion 41 counts
the received trigger, and sends the trigger to the laser oscillator
32 if a count value is valid (a predetermined count value is not
reached). When the laser oscillator 32 receives the trigger from
the trigger generating apparatus 40 through the trigger counting
portion 41, the laser oscillator 32 immediately outputs the laser
beam 27 by only one pulse with a pulse width of 200 .mu.s or less.
The laser beams 27 including optional successive three pulses are
outputted in such a manner, and are sequentially reflected at any
one of the two rotary choppers 39 and the reflection mirror 36 so
as to be introduced to the three machining stations. Through a ZnSe
lens 9, the three printed boards 1F are respectively irradiated
with the laser beams 27. When the predetermined number of triggers
is counted, the trigger counting portion 41 disables the next and
later triggers to the laser oscillator 32, and sends a table moving
trigger to the control unit 38 of the XY table 37. When the XY
table 37 is completely positioned, the trigger counting portion 41
enables a trigger again by receiving a positioning completion
signal from the control unit 38 of the XY table 37.
[0153] FIG. 29 is a time chart of the trigger and laser pulses in
the embodiment 12. As shown in FIG. 29, the machining stations are
respectively irradiated with the laser beam 27 shown by any one of
reference numerals ST1, ST2, and ST3 once every generation of any
one of three triggers from the trigger generating apparatus 40. For
example, when the two rotary choppers 39 are rotated such that the
trigger from the trigger generating apparatus 40 can have a cycle
of 5 ms or more, the machining stations are respectively irradiated
with pulses at time intervals of 15 ms or more. As seen from a
relationship shown in FIG. 6, it is thereby possible to drill for a
good hole with a small amount of a char layer. When the beam
irradiation is required m times for each drilling and sequential
drilling is made for other holes, the predetermined number of
triggers in the trigger counting portion 41 may be set to
(3.times.m). It is thereby possible to machine the entire areas of
the three printed boards 1F by repeating the beam irradiation and
movement of the table.
[0154] As set forth above, according to the embodiment 12, there is
no decrease in energy of the laser beam 27 in the respective
machining stations. Further, the speed of rotation of the rotary
choppers 39 is set such that the laser beams 27 can be transferred
to the machining stations at time intervals of 15 ms or more. It is
thereby possible to concurrently provide in the plurality of
printed boards 1F high quality platable holes without projection of
glass cloth, and more rapidly machine the printed board 1F
containing the glass cloth, resulting in a significant improvement
of productivity. Further, the combination of the beam scanner
apparatus 34 in the embodiment 11 and the embodiment 12 can reduce
a time required for the movement of the table, and enables higher
speed machining of the plurality of printed boards.
Embodiment 13
[0155] FIG. 30 is a perspective view showing a structure of a
carbonic acid gas laser oscillator for machining a wiring board
according to the embodiment 13 of the present invention. In the
drawing, reference numeral 42 means a pair of discharge electrodes
to form a discharge space 43 in a gap therebetween, 44 is a
resonator mirror, 45 is a gas flow serving as laser medium, 46 is
an optical axis of a laser beam 27, and 47 is an aperture to select
the degree of mode of the laser beam 27. The unit including the
optical axis 46 of the laser beam 27, the gas flow 45, and a
direction of discharge in an orthogonal relationship is typically
referred to as three-axes orthogonal type laser oscillator.
[0156] A description will now be given of the operation.
[0157] Discharge power is fed from the discharge electrodes 42 to
form the discharge space 43 into which the gas flow 45 flows. A
molecule in the gas flow 45 is excited by energy of discharge to
have a gain to light. When the discharge space 43 is formed in a
stationary manner, there is formed a stationary gain distribution
having a peak in the vicinity of the downstream of the discharge
space 43 as shown in FIG. 31(a). Therefore, in order to efficiently
provide stationary laser oscillation, that is, successive output
(CW output), it is necessary to dispose the optical axis 46 and the
aperture 47 across a line which vertically travels in the
downstream of the discharge space 43 providing the maximum gain
distribution as shown in FIG. 31(b). For the purpose, in the prior
art, a typical three-axes orthogonal type of carbonic acid gas
laser oscillator has the above structure.
[0158] However, unlike the prior art, there is provided the
carbonic acid gas laser oscillator for machining the printed board
according to the embodiment 13 of the present invention having a
structure as shown in FIG. 32. In the structure, the aperture 47 is
disposed in the range in that the aperture 47 does not extend off
the discharge space 43, and the optical axis 46 is disposed on a
line vertically travelling on the farthest upstream side of the
discharge space 43.
[0159] In a conventional structure shown in FIG. 31(b), it can be
considered that energy of an excited molecule at a point A in the
upstream of the discharge space 43 is converted into the laser beam
27 at a time of reaching a point B. Further, it can be seen that an
excited molecule at the point A at the moment at which the
discharge is stopped is converted into the laser beam 27 after the
elapse of a time of (X/V) (where V is a gas flow rate, and X is a
distance from the point A to the point B). Therefore, when the
optical axis 46 is disposed in the downstream of the discharge
space 43 as shown in FIG. 31(b), a time required for disappearance
of the laser beam 27 after the discharge is stopped becomes longer,
and a fall of a laser pulse at a time of pulse oscillation becomes
slower than would be in case where the optical axis 46 is disposed
in the upstream of the discharge space 43 as in the embodiment 13
shown in FIG. 30. For example, in the conventional laser oscillator
with a 30 mm distance between the point A and the point B, that is,
a 30 mm width of the discharge electrode 42 and a gas flow rate of
80 m/s, a fall time of the laser pulse becomes 375 .mu.s. Even if a
fall time of the discharge power itself is reduced, it is
impossible to reduce the fall time of the laser pulse.
[0160] On the other hand, according to the embodiment 13 shown in
FIG. 32, the aperture 47 is disposed in the range that the aperture
47 does not extend off the discharge space 43, and the optical axis
46 is disposed on the line vertically travelling on the farthest
upstream of the discharge space 43. For example, for a 6.5 mm
distance between the point A and the point B and the gas flow of 80
m/s, it is possible to provide an 81 .mu.s fall time of the laser
pulse. In this case, it is necessary to provide a sufficiently
short fall time of the discharge power because a fall time of the
laser pulse is affected by a longer fall time of the discharge
power than the fall time of the pulse. When the optical axis 46 is
disposed as in the embodiment shown in FIG. 32, the fall time of
the discharge power is preferably set to 50 .mu.s or less. When the
optical axis 46 is disposed as in the embodiment 13 shown in FIG.
32, a rise time of the discharge power has an effect on a rise time
of the laser pulse. Thus, the rise time of the discharge power is
preferably set to 50 .mu.s or less in order to obtain a narrow
pulse width of 200 .mu.s or less.
[0161] As set forth above, according to the embodiment 13, it is
possible to provide the laser pulse having a sharp rise, a sharp
fall, and the pulse width of 200 .mu.s or less, which can not be
provided by the conventional carbonic acid gas laser. The machining
can be made without projection of glass cloth and generation of a
char layer by applying the laser pulse to the machining of the
printed board.
[0162] As set forth above, according to the present invention,
there is provided the laser beam machining method for the wiring
board, including the step of irradiating the machined portion of
the wiring board with the pulsed laser beam for the beam
irradiation time ranging from 10 to 200 .mu.s and with the energy
density of 20 J/cm.sup.2 or more. As a result, there is an effect
in that good and fine machining can be made in, for example, the
drilling for the through-hole and the blind via hole, the grooving,
and the cutting for the outside shape with respect to the board
made of the composite material having inclusion such as glass
cloth.
[0163] According to the present invention, there is provided the
laser beam machining method for the wiring board, including the
step of irradiating the same machined portion of the wiring board
with the pulsed laser beam with intervals of the beam irradiation
pausing time of 15 ms or more and the energy density of 20
J/cm.sup.2 or more. As a result, there are effects in that the
conduction hole can be obtained with the high aspect ratio which
can not be obtained by the single pulse, projection of the glass
cloth can be reduced, and the wiring board containing the glass
cloth can rapidly and accurately be machined even in case of the
multi-pulse irradiation.
[0164] According to the present invention, there is provided the
laser beam machining method for the wiring board, including the
step of irradiating the same machined portion of the wiring board
with the pulsed laser beam with the plurality of pulse groups
respectively including the plurality of pulses respectively having
the energy density of 20 J/cm.sup.2 or more at intervals of the
pulse group interval irradiation pausing time longer than the
predetermined beam irradiation pausing time. As a result, there are
several effects of machining for the conduction hole in a shorter
time than would be in the machining employing the single pulse
frequency, prevention of the temperature rise at the machined
portion, a reduction in gradation of the temperature gradient with
respect to the depth distance from the surface of the machined
portion, and a reduction in projection of the glass cloth.
[0165] According to the present invention, there is provided the
laser beam machining method for the wiring board, in which the
predetermined beam irradiation pausing time is 4 ms or more, the
number of pulses in the pulse group is 4 or less, and the pulse
group interval beam irradiation pausing time exceeds 20 ms. As a
result, there are effects of reduced generation of the char layer
in the machined hole, and good and fine machining in the drilling
for the through-hole and the blind via hole, the grooving, the
cutting for the outside shape, and so forth.
[0166] According to the present invention, there is provided the
laser beam machining method for the wiring board, including the
step of, at a time of scanning the surface of the wiring board
while irradiating the machined portion of the wiring board with the
pulsed laser beam, scanning by the laser beam such that the
machined portion is not continuously irradiated with the laser beam
over 4 pulses and at intervals of the beam irradiation pausing time
less than 15 ms. As a result, there are effects in that it is
possible to reduce generation of the char layer in the machined
hole, and increase the machining speed while keeping the same
machining quality as that in machining by positioning the beam at
the machined portions.
[0167] According to the present invention, there is provided the
laser beam machining method for the wiring board, including the
steps of providing the 1 mm beam diameter on the surface of the
machined portion, and scanning the surface of the wiring board at
the scanning speed ranging from 8 to 6 m/min while irradiating the
machined portion with the laser beam for the beam irradiation time
ranging from 10 to 200 .mu.s and at intervals of the beam
irradiation pausing time of 2.5 ms. As a result, there are effects
in that it is possible to increase the machining speed while
keeping the same machining quality as that in machining by
positioning the beam at the machined portions, and provide good and
fine machining such as drilling for the blind via hole in the board
made of the composite material having inclusion such as glass.
[0168] According to the present invention, there is provided the
laser beam machining method for the wiring board, including the
steps of setting the laser beam to have the square spot effective
in the machining of the machined portion of the wiring board, and
scanning the surface of the wiring board while irradiating the
machined portion of the wiring board with the pulsed laser beam. As
a result, there is an effect in that the machining speed can be
more increased with good machining quality than would be in case of
the circular beam.
[0169] According to the present invention, there is provided the
laser beam machining method for the wiring board, including the
steps of setting the square spot of the laser beam on the machined
portion to have the size of 0.9 mm.times.0.9 mm, and scanning the
surface of the wiring board with the scanning speed of 6 m/min and
the scanning pitch of 200 .mu.m while irradiating the machined
portion with the laser beam for the beam irradiation time ranging
from 10 to 200 .mu.s and at intervals of the beam irradiation
pausing time of 1.25 ms. As a result, there are effects in that
higher quality can be kept than would be in case of the circular
beam, and the machining speed can be increased.
[0170] According to the present invention, there is provided the
laser beam machining method for the wiring board, including the
steps of previously removing the metallic layer on the wiring board
at the portion corresponding to the machined portion of the wiring
board, forming the base material removed portion through the
machining by irradiating the base material of the machined portion
with the laser beam through the metallic layer removed portion, and
additionally irradiating the base material removed portion and the
periphery of the base material removed portion, or only the
periphery of the base material removed portion with the laser beam.
As a result, there is an effect in that the rigid additional
deposit generated during the machining can simply be removed
without the complicated step such as wet etching even in the
machining having large volumes of removed materials.
[0171] According to the present invention, there is provided the
laser beam machining method for the wiring board, including the
steps of previously removing the metallic layer on the wiring board
at the portion corresponding to the machined portion of the wiring
board, forming the base material removed portion through the
machining by irradiating the base material of the machined portion
with the laser beam through the metallic layer removed portion, and
additionally irradiating and scanning the base material removed
portion and the periphery of the base material removed portion, or
only the periphery of the base material removed portion with the
laser beam having a smaller peak output than that of the above
laser beam at a higher scanning speed than a scanning speed during
first laser beam irradiation. As a result, there is an effect in
that the rigid additional deposit caused during the machining can
simply be removed without the complicated step such as wet etching
even in the machining having large volumes of removed
materials.
[0172] According to the present invention, there is provided the
laser beam machining method for the wiring board, including the
step of, at the time of previously removing the metallic layer on
the wiring board at the portion corresponding to the machined
portion, partially removing the metallic layer such that the laser
beam can reach only the outer periphery of the base material
removed portion to be formed by irradiating the base material of
the machined portion with the laser beam. As a result, there is an
effect of good machining causing no failure such as peeling of the
metallic layer even in case of machining with the removed portion
larger than the non-removed portion.
[0173] According to the present invention, there is provided the
laser beam machining method for the wiring board, including the
steps of partially removing the metallic layer such that the laser
beam can reach only the outer periphery of the base material
removed portion to be formed by irradiating the base material of
the machined portion with the laser beam, and scanning the surface
of the wiring board with the scanning speed of 8 m/min and the
scanning pitch of 100 .mu.m while irradiating the machined portion
with the laser beam for the beam irradiation time ranging from 10
to 200 .mu.s and at intervals of the beam irradiation pausing time
of 2.5 ms. As a result, there is an effect of good machining
causing no failure such as peeling of the metallic layer because
the base material removed portion is not entirely removed even in
case of machining with the base material removed portion larger
than the non-removed portion.
[0174] According to the present invention, there is provided the
laser beam machining method for the wiring board, including the
steps of previously removing the metallic layer on the wiring board
at the portion corresponding to the machined portion, and flowing
the gas in the direction from the laser beam scanning start point
to the laser beam scanning end point in the machined portion at the
time of the machining by irradiating the base material of the
machined portion with the laser beam while scanning by the laser
beam through the metallic layer removed portion. As a result, there
are effects in that it is possible to effectively eliminate the
adverse effect of the residual additional deposit on the machining
even in the machining with large volumes of removed materials, and
significantly reduce the area having the residual additional
deposit.
[0175] According to the present invention, there is provided the
laser beam machining method for the wiring board, including the
steps of forming the metallic layer having the desired shape by
partially removing the metallic layer by pulse irradiation with the
laser beam having the sufficient intensity to melt and remove the
metallic layer on the wiring board, and additionally irradiating
the machined portion of the wiring board through the metallic layer
removed portion with the laser beam having the insufficient
intensity to melt the metallic layer and the beam irradiation time
ranging from 10 to 200 .mu.s, and including the plurality of pulses
forming a train at intervals of the beam irradiation pausing time
of 15 ms or more. As a result, there is an effect in that rapid and
accurate machining can be made simply by the laser beam machining
step even in the wiring board having the surface coated with the
copper foil and including the glass cloth.
[0176] According to the present invention, there is provided the
laser beam machining method for the wiring board, including the
step of exposing the machined portion by previously removing,
through another machining method such as etching, the metallic
layer positioned at the target position for laser beam irradiation
and in the range smaller than the area to be machined. As a result,
there are effects of improved absorption of the laser beam, and
efficient and more stable drilling.
[0177] According to the present invention, there is provided the
laser beam machining method for the wiring board, including the
step of previously making the surface roughening to the surface of
the metallic layer on the surface of the wiring board before the
laser beam irradiation. As a result, there are effects in that the
metallic layer can be removed by improving the absorption of the
laser beam even in case of low peak output of the laser beam, and
efficient and more stable drilling can be made.
[0178] According to the present invention, there is provided the
laser beam machining method for the wiring board, including the
step of, at a time of pulsed laser beam irradiation while
sequentially positioning the spot of the laser beam at the target
positions on the wiring board in synchronization with the pulse
frequency of the laser beam, providing the time interval of 15 ms
or more between the two optional successive pulsed laser beams for
irradiation of the respective target positions irrespective of the
pulse frequency by irradiating another target position with the
pulsed laser beam outputted for the time interval therebetween. As
a result, there is an effect in that the high quality platable hole
can be provided with little formation of the char layer and no
projection of the glass cloth because the beam irradiation can be
made with the beam irradiation pausing time of 15 ms or more
ensured for each machined portion even when the laser beam having
high pulse frequency is used. Further, there is another effect in
that the scanning frequency of the spot of the laser beam can be
increased to its limitation so as to enable the high-speed
drilling, and drill for many holes in a short time, thereby
significantly improving productivity of the wiring board.
[0179] According to the present invention, there is provided the
laser beam machining method for the wiring board, including the
steps of providing the plurality of machining stations on which the
wiring boards to be machined are mounted, sequentially dividing the
pulsed laser beam outputted from the laser oscillator among the
plurality of machining stations for each pulse, and introducing the
pulsed laser beam into the plurality of machining stations at the
time intervals of 15 ms or more. As a result, there are effects in
that rapid machining for the conduction hole can be made at the
plurality of machining stations without a reduction in quality of
the machined hole, and productivity of the wiring board can
significantly be enhanced.
[0180] According to the present invention, there is provided the
laser beam machining method for the wiring board, in which the
carbonic acid gas laser is used as a light source of the laser
beam. With the use of the carbonic acid gas laser having high
absorption coefficient shown by the glass, there is an effect of
rapid and accurate machining even in the wiring board containing
the glass cloth, which is difficult to machine in other lasers.
[0181] According to the present invention, there is provided the
laser beam machining method for the wiring board, in which the
wiring board contains the glass cloth. As a result, there are
effects in that projection of the glass cloth can be reduced, and
the wiring board containing the glass cloth can rapidly and
accurately be machined.
[0182] According to the present invention, there is provided the
laser beam machining apparatus for the wiring board, including the
optical mechanism to change a direction of the laser beam and move
the laser beam on the wiring board while sequentially positioning
the spot of the laser beam at the target positions on the wiring
board, and the control mechanism for synchronous control between
the pulse oscillating operation of the laser beam oscillator and
the operation of the optical mechanism, and control of the optical
mechanism such that the time interval can be set to 15 ms or more
between the two optional successive pulsed laser beams for
irradiation of the target positions irrespective of the pulse
frequency of the laser oscillator. As a result, there is an effect
in that the high quality platable hole can be provided with little
formation of the char layer and no projection of the glass cloth
because the beam irradiation can be made with the beam irradiation
pausing time of 15 ms or more ensured for each machined portion
even when the laser beam having high pulse frequency is used.
Further, there is another effect in that the scanning frequency of
the spot of the laser beam can be increased to its limitation so as
to enable the high-speed drilling, and drill for many holes in a
short time, thereby significantly improving productivity of the
wiring board.
[0183] According to the present invention, there is provided the
laser beam machining apparatus for the wiring board, including the
optical mechanism to sequentially divide the pulsed laser beam
outputted from the laser oscillator among the plurality of
machining stations for each pulse and introduce the pulsed laser
beam into the plurality of machining stations for each pulse at
time intervals of 15 ms or more, and the synchronization control
mechanism for synchronous control between the dividing operation of
the optical mechanism and the pulse oscillating operation of the
laser oscillator. As a result, there is an effect in that rapid
machining for the conduction hole can be made at the plurality of
machining stations without a reduction in quality of the machined
hole.
[0184] According to the present invention, there is provided the
laser beam machining apparatus for the wiring board, including the
optical mechanism provided with the at least one rotary chopper
rotated at the predetermined speed of rotation, having the
plurality of reflection surfaces and the plurality of passing
portions at positions equally dividing the periphery about the axis
in the plane perpendicular to the rotation axis, and the
synchronization control mechanism provided with the trigger
generating apparatus to generate the trigger each time all the
equally divided areas including the plurality of reflection
surfaces and the plurality of passing portions in the rotary
chopper respectively move across the optical axis of the laser
beam. As a result, there is an effect in that rapid machining for
the conduction hole can be made at the plurality of machining
stations without a reduction in quality of the machined hole.
[0185] According to the present invention, there is provided the
carbonic acid gas laser oscillator for machining the wiring board,
in which the length of the discharge space in the gas flow
direction is equal to or more than the width of the aperture, the
optical axis passing through the center of the aperture is set to
be positioned in the range that the entire area of the aperture
does not extend off the area extending in the gas flow direction of
the discharge space and on the farthest upstream side of the gas
flow, and the rise time and the fall time are set to 50 .mu.s or
less in the discharge power fed to the discharge space. As a
result, there are effects in that it is possible to reduce the rise
and the fall of the laser beam, and obtain the laser beam with the
short beam irradiation time suitable for machining of the wiring
board.
[0186] While preferred embodiments of the invention have been
described using specific terms, such description is for
illustrative purposes only, and it is to be understood that changes
and variations may be made without departing from the spirit or
scope of the following claims.
* * * * *